1. Field of the Invention
This invention relates to engine fuel injectors and more particularly to such an injector which can alternatively be operated to inject either liquid or gaseous fuel into an engine.
2. Description of the Related Art
Dual fuel injection systems for engines are commonly used to enable the use of either gasoline or a gaseous fuel. Gaseous fuel has advantages over gasoline in that its cost is generally lower and it produces an exhaust gas having substantially lower pollutants than that of gasoline. However, it is desirable to also utilize gasoline in view of the fact that it is readily available on the road which is not the case with gaseous fuel.
In prior art dual fuel systems, two separate fuel injectors and associated electronic control systems are generally required, one for each of the fuels. Such a prior art system is described in U.S. Pat. No. 5,450,832 issued Sep. 19, 1995 to Graf. The use of a separate fuel injector for each of the fuels increases both the cost and complexity of the system and also often has the disadvantage of requiring indirect routing for the liquid fuel to the engine manifold which leads to partial vaporization of the fuel which hampers the control of fuel delivery and leads to fuel waste.